Telephony.



E. R. CORWIN.

TELEPHONY.

APPLICATION FILED JAN-16,1914.

2 SHEETSSHEET I.

jg. Z r

Patented May 30, 1916.

E. R. CORWIN.

TELEPHONY.

APPLICATION FILED JAN. 16. 1914.

Patented May 30, 1916.

2 SHEETSSHEET 2.

snares rarnnr clarion ELMER R. CGFJWIN, F CHICAGQ, ILLINQIS, ASSIGNOR,BY MESNE ASSIGNMENTS, TU) FRANK 3B. COOK COMIPANY', UTE CHICAGO,ILLENOE, A CDRBORATIQN G ILLINOIS.

TELE'BHQNY,

menace.

Specification of Letters Patent.

Patented May 3t 1916,

To all whom it may concern J Be it known that 1, Emma lit. Conwrn,citizen of the United States, residing at Chicago, in the county of{Cook and State of Illinois, have invented a certain new and 1 ing fromvonetelephone station to an exchange, a second telephone line extendingfrom another telephone station, two equipments ,each for connecting thefirst telephone line with the second telephone line, said telephonelines having means cooperating with these equipments to this end,selecting means for associating either of said equipments with the firstline, and means at the telephone station of the first line for operatingsaid selecting means arbitrarily to associate eitherpr" said equipmentswith the first line.

My invention has for another or" its objects the provision or atelephone exchange system in'which there is included one telephone lineextending from one telephone station to an exchange, other telephonelines extending from other telephone stations, two equipments wherebythe first telephone line may be connected with the other telephonelines, said telephone lines having means cooperating these equipments tothis end, and two selectors individual to the aforesaid equipments andeach individually controlled the of the first line to associate theequipment individual thereto with the first line.

The aforesaid equipments are desirably, though not necessarily, distincttheir nature and one embodiment oi" the invention one of theseequipments is operator controlled and the other of said equipmentsincludes electro-magnetic mechanism by which a calling subscriber mayextend his line into connection with the called line.

vthe preferred embodiment of my invention a selector is employed whichis individual to each equipment and a controlling means is provided atthe station of the first aforesaid.v line individual to each scinventionthe subscriber who is enabled to operate electromagnetic switchingmechanism to extend or take part in extending his telephone line isapprised of the association of the line extendingelectro-magnetioswitching mechanism with his telephone line either by the operation ofthe calling subscribers receiver orby the manifestation of a signalathis station through the aid of some other responsive signal conveyingdevice.

I will explain my invention more fully by reference to the accompanyingdrawings showing one preferred embodiment thereof and in which v Figures1 and'2 taken collectively illustrate a telephone exchange system havingexchange equipment whereby either of the calling subscribers maycomplete the connections they desire with called lines or wherebyoperators may cooperate with the calling subscribers to this end; andFig. 3 is a detail of a part of the substation equipment.

At the exchange 1 have illustrated selectingrelays or eleotro-ma'gnets land 2 individual to each line which are so electrically and mechanicallyindependent as to enable each to perform its. operating functionswithout occasioning the other to perform an operating function. ,Therelays l are adapted when operated to associate their lines withequipment that will extend such lines to operators positions havingusual or suitable operator controlled equipment "for extending callinglines such" as plugs 3 and jacks The relays 2 are adapted when operatedassociate their lines with equipment, under the control of callingsubscribers, that will extend such lines into cormection with desiredlines, such equipment being any usual or suitable so-called automatictelephone exchange equipment. Each calling subscriber has means i'orselecting, for operation, one or the other or" the relays l, 2,according to therouting or equipment which is to be employed forconnecting his linewith the called line.

Two of many subscribers lines are illustrated, each having a telephoneswitch hook 5, telephone receiver 6, telephone transmitter 7, animpedance coil 8 in series with the transmitter and in shunt of thereceiver, and

a signal bell 9 and condenser 10 included in serial relation in bridgeof their telephone line. When the receiver is upon its switch hook suchswitch hook is. separated from its contact to cut the receiver andtransmitter out of circuit, the switch hook including the transmitterand receiver in circuit when the receiver is removedv from the switchhook. A switch 11 is carried by the switch hook 5 and engages itscontact when the switch hook is free of its receiver. The dial leverswitch arm 12 is adapted to be moved by a calling subscriber over aseries of electrically connected contact buttons 13 and againstthe'force of a restoring spring 14 which operates to restore the switcharm to normal when such switch arm is released. An additional switch arm15 is coupled with the arm 12 and turns therewith. A segmental contactplate 16 is in position to be superposed by the switch arm 15 when theswitch arm 12 engages the second and each subsequent button but theswitch arm 15 is not in electrical connection with the contact 16 untilit has been depressed by the button 17. If the calling subscriber wishesto have his connection extended with the aid of the magnet 1, he simplyremoves his telephone receiver from its switch hook but if he wishes tohave his connection extended with the aid of the magnet 2, he brings theswitch arm 12 into engagement with that one of the buttons 13 whichcorresponds to the called 7 line depresses the button 17 to bring. the

switch arm 15 into engagement with the grounded contact 16, andthereafter removes his telephone receiver from its switch hook wherebythe magnet or relay '2 is energized'to set the automatic equipment intooperation automatically to connect the desired line with thecallingline.

The operations which result consequent upon the energization of therelay 1 and due to the mere removal of the telephone receiver 6 of thecalling subscriber will first be described. When the receiver 6 ismerely removed a circuit is established traceable from the commongrounded battery 18, through the winding of relay 2 which is of lowresistance in comparison with the resistance of the relay 1, theintermediate armature switch of the cutofl' relay 19 and its normalcontact, the lower side of the calling .line, the switch ll'at thecalling station and its contact, the low resistance path that includesthe buttons 13, the switch arm 12 normally engaging the uppermost one ofthe buttons 13, the switchhook 5, the contact of this switch hook, theelements 6, 7 and 8,, the upper sides of the calling line, the uppermostarmature switch of the cutoff relay 19 and the normal contact of thisarmature switch, the winding of relay 1, to ground. The relay 1 is nowenergized to remove its armature ca switch from engagement with itsnormal contact into its engagement with its alternate contact whereupona circuit is established traceable from the grounded battery 18, throughthe relay 20 which is common to agroup of lines, the armature switch. ofrelay 1 and its alternate contact, to ground. Thearmature switch ofrelay 20 establishes a circuit traceable from the grounded battery 18,through'the lower armature switch of relay 21 and it's contact, thearmature switch of relay 20 and its contact, the winding of relay 22,the wiper 23, a waiting contact 24 (there being as many waiting contactsas there are link connectors in an operators position, there being arelay 20, a relay 21, a relay 22, and a wiper switch structure having aWiper 23 individual to each operators position), the lowermost armatureswitch of a relay 25 and its normal contact (each link connector havinga plug 3 being provided with a relay 25 individual thereto) a waitingcontact engaged by the wiper 26 and pertaining to some line other thanthe calling line and whose relay 1 is deenergized, to ground by: way ofthe armature switch and normal contact of the relay '1 of such otherline. Each link connector having aplug 3 has a driving magnet 27individual thereto and this driving magnet has a circuit established bythe relay 22 which is traceable from the grounded battery 18, throughthe interrupter relay 28 (individual to the switch having the wiper 23),the armature switch and contact of this interrupter relay, the upperarmature switch of relay 22 and its contact. the wiper 29 companion tothe wiper 23, the

waiting contact 30 companion to the waiting contact 24c, the/winding ofdriving magnet 27, to ground. The magnet 27 isthus intermittentlyenergized to drive the wiper 26 and other wipers compahion thereto untilthe wiper 26 is brought into engagement with the waiting contactbelonging to a calling line whose relay 1 is energized whereupon thecircuit for the relay 22 is opened at the armature switch of suchenergized relay 1 whereby the circuit of motor magnet 27 is opened atthe released upper armature switch of relay 21 to cause-the wipers 26 toremain at rest.

It is under'stoodthat the wiper 26 and its companion wipers are providedwith waiting contacts that are individual to the different lines of onegroup and that the waiting contacts pertaining to the wiper26 aresufiiciently close to permit the wiper toen gage one waiting contactbefore leaving the preceding waiting contact. The wipers 31,

32 and 33 companion to the wiper 26 are now also brought into engagementwith their waiting contacts.. The calling tele-- phone line is nowextended, by way of, the wipers 32 and 33, into connection with the twoupper armature switches of relay 25 individual to the selected linkconnector having a connecting 'plug'3. j When the relay 22 has beendeenergized in order to enable the calling line to become connected withthe upper ar'mature switches of the relay 25 in the operation ofautomatically extending the calling line intdconnection with theselected 2 link, the attendant operator is. apprised of such linkselection by any suitable means and to this end I have indicated but donot wish to be limited to 'a'visual signal lamp which, at the time of'deenergization of the relay 22, is included in the circuit trace ablefrom the grounded battery 18 through the lower armature switch of therelay 21 and its contact, the armature switch of relay 20 and itscontact, the lower armature switch of relay 22 and its 'contact,thewiper 36, and

the waiting contact. engagedthereby and individual to the operatorsposition and constituting a terminal of the lamp 35, thence to ground.The operator, in response to the signal manifested by the signal device35, manipulates her listening key 27 for the purpose of including hertelephone set 38 in circuit with the calling line to ascertain thenumber of the line wanted, the depression of the listening key resultingin the energization of therelay 25 whose upper armature switches engagetheir contacts to extend the calling line into connection with theselected operators telephone set. The

' circuit which is established through the relay 25 is traceable fromthe grounded battery 18, through the lower winding of relay 25, theoperators telephone set by way of the listening key, the upper windingof relay 25 (the windings of. relay 25 being on mulative), to ground.When the relay 25 is energized a circuit is established traceable fromthe grounded battery 18, through the cutoff relay 19, the: wiper 31and-its waiting contact, the lower-intermediate armature switch of relay25 and its contact, the upper winding of relay. 39, to ground.

The cutoff relay '19 is thus energized to atter switch having the wipers23, 29 and 36 and which is common to a group of link connectors is nowset into operation owing to the establishment of a circuit traceablefrom the grounded battery 18, through the winding of relav 21, the wiper40,- the waiting contact of the wiper 40 which is individual f to theselected link (it being understood that there are as many sets ofwaiting contacts for the wipers 23, 29, 36 and 40 as there are linkconnectors in a group, each set being individual to a link connector ofsuch group), the lowermostarmature switch of relay 25 and its alternatecontact, the wiper 26 and its waiting contact, the upper armature switchof relay land its normal contact, to ground. .The relay'21 isnowenergized to establish a' circuit for the motor magnet 41 traceable fromthe grounded battery 18, through the interrupter relay 28 and itsarmature switch and contact, the upper armature switch of relay 21 andits contact, to the grounded winding of the motor magnet 41. The motormagnet 41 now op- .erates until the Wipers 23 etc. controlled therebyare brought into engagement with waiting contacts pertaining to someidle link connector of its group, that is until the wiper 40 engages awaiting contact that extends to the alternate contact of the lowermostswitch of some relay 25 that is deenergized, and is therefore notconnected with such lowermost switch, whereupon the circuit of the relay21 is opened to open the circuit of the motor magnet 41.

The selected operator will now apply the tip of the selected plug 3 tothe thimble of a multiple jack 4 appearing at her position and belongingto "the desired line. If the desired line is idle there will be noimani-' festation of noise in the receiver of the telephone outfit 38. vIf the desired line has been previously taken for use a test circuit isestablished traceable from the grounded battery 18 through the windingof the cutofi" relay 19 of the tested line, the thi-mble of the testjack 4, the tip of the test plug, the uppermost armature switch of relay'39 and its contact, the intermediate switch spring of the listening key37 and its alternate contact, to the grounded induction coil winding.42, from which winding current is induced into the vcompanion inductioncoll winding 43, the current in this latter winding operating to make anoise in the testing oper ators' receiver. If the line wanted is freethe operator will insert the selected plug3 within the test jack tocomplete the conmotion. between calling and called lines. The heel ofthe inserted plug 3 establishes a circuit for the relay 19 of the calledline, which circuit is traceable from the grounded battery 18, thewinding 19 of the cutofi relay of the called line, the thimbleof thejack containing the plug, the heel of the plug, the lowermost armatureswitch of relay 39 512% its contact, to the grounded resistance Thecutofi relay 19 of the calle line is now energized so that when thecalled subscriber responds to the signal manifested at his bell 9he willnot occasion.

the effective operation of any line extending apparatus at the exchange.The called line its 4, meters of alternating current finding passagefrom the grounded generator 45, the lower spring of the ringing key 46and its alternate contact, the sleeve of the employed plug 3, the sleevespring of the jack 4 receiving such plug, one side of the called line,the called bell 9 and condenser at the called station,

- the other side of the called line, the tip spring of said jack, thetip of the employed plugB, the upper spring of the ringing key 46, thealternate contact of this spring, to.

ground. When the key 37 is released a talking circuit is establishedbetween the calling 1 and called stations by way of the two uppersprings of the key 37. Talking battery current is fed to the substationsthrough the lower windings of relays 25 and 39 whereby these relays aremaintained energized during an established connection, theselowerwindings being under control of a calling and called subscriberrespectively, to maintain their armature switches attracted until theswitch hooks at the corresponding stations are engaged by the receiversthereat.

When the receivers at the two connected stations are restored to theirswitch hooks the previously employed link connector is restored to anidle condition ready for selection by another calling line when themaster switch having the wipers 29, etc. place it in condition for suchselection, it being permissible to allow the plug 3 to remain in thejack.

If the calling subscriber should for any reason select a routing to thecalled line by way of the automatic equipment illustrated in the lowerportions of the drawings, such calling-subscriber will place the switcharm 12 upon the button 13 corresponding to the number of the desiredline if such number be less than ten or to the first digit of the numberof the desired line if such number be in excess of nine, the firstbutton at the top 'ofthe row constituting the normal buttonwhile thesecond button corresponds to digit one, the gaps between the buttonsbeing so spaced apart that the arm 12 will break circuit in passing fromone button to another to furnish impulses on the return movement of thearm. When the arm 12 'has thus been engaged with such a digit button 13,the push button 17 is depressed to bring the switch arm 15 intoengagement switch hook and the button 17 is not dc pressed, this buttonbeing only momentarily depressed, when the arm 12 has been engaged withthe first button 13. When the arm 15 has been thus momentarily connectedwith the contact 16 a circuit is established traceable from thegrounded-battery 18, through the winding of the relay or magnet 2, theintermediate armature switch of the cutoff relay 19 belonging to thecalling line and the normal contact of this switch, the lower side ofthe calling line, the switch 11 at the calling station and the contactof this switch, the set of buttons 13, the switch arm 12, the switch arm15, the segmental contact plate 16, to ground. The magnet 2 is thusenergized to attract its armature switch from its normal contact intoengagement with its alternate contact. The relay 1 companion to therelay 2 is short circuited when the contact plate .16 is included in theestablished circuit so that this relay 1 is not energized when thecompanion relay 2 is energized.

'The automatic equipment includes some apparatus which is structurallysimilar to some of the equipment employed in association with themanually controlled link connectors previously described and parts. ofthe automatic equipment which-are similar to parts of the otherequipment are given similar characters of reference with prime exponentsadded thereto. As will be apparent from an inspection of the drawingsthe electrical environment of these parts of the automatic equipment isgenerally similar to the correspondingly numbered parts of the otherequipment and a further detail description of these parts of theautomatic equipment is not essential.

When the relay 2 is energized a circuit is established traceable fromthe grounded battery 18, through relay 20, to the grounded armatureswitch of relay 2 by way of its alterhate contact. The armature of relay20 now establishes a circuit for relay 22 by way of the extreme lefthand switch of relay 47 and its contact, the wiper 26 and a waitingcontact engaged by this wiper that is connected with the normal contactof the armature switch of a deenergized relay 2 belonging to some otherline. The motor magnet .27 is now included in circuit with the armatureswitch of the interrupter relay 28 and the winding of this relay to stepthe wipers 26 etc., around until these wipers become connected orassociated with jthecallin line to extend the calling line'intoi'assocmtion with the armature switches of relay 25 individual toan idle link conmotor that automatically has, acc ess to the switches ofrelay 47 the normal contact of the uppermost armature switch of relay 25to the: grounded resistance 48.

subscriber that he may release the button masses desired line whereafterthe relay 22 is deenergized at the attracted armature switch of therelay 2 belonging to the calling line. The relay 47 is now energized bya circuit traceable from the grounded battery 18 through the attractedarmature switch of relay 20 and its contact, the lower armature switchof the now deenergizedrelay 22 and its contact, the wiper, 36 and thewaiting contact individual to the selected link connector (the wiper 36and its companion having a number ofvsets of waiting contacts eachindividual to a link connector) the winding of relay 47 toground. Acircuit is established by the fourth armature switch from the left,ofrelay 47, for the cutofi' relay 19 of the calling line whereby themagnets 1 and 2 of the calling line are removed from connection with thecorresponding armature switches of said cutofi relay 19, this circuitbeing traceable from the grounded battery 18, the winding of said relay-19, the wiper 31 and its engaged waiting contact, -said= armature switchof relay 47, The two upper armature switches of said relay 19 are now in-engagement with their alternate contacts to bring the calling linesides into connection with the two upper armature switches of relay 25The second of the armature switches from the left, of relay 47 placesthe battery 18 and relay 49 in circuit with the telephone outfit at thecalling station to indicate to the calling which isheld depressed untilthe: battery 18is thus included in circuit with the telephone receiverat the calling station for the purpose of establishing a circuit throughthe sluggishly operating relay 49, this circuit being traceable from thegrounded battery 18, through the winding of relay49, the second-from theleft of the armature said armature switch, the wiper 33 the waitingcontact engaged by this wiper, the uppermost armature switch of relay 19and its alternate contact, the upper side of the calling line, thetelephone bridge at the callswitch arm 15, segmental contact plate 16,to ground, whereafter the dialing operations may be continued, since therelease of the button 17 is followed by the automatic elevation of theswitch arm 15 from the contact plate 16.

After the button 17 is released the switch 12 is automatically restoredto normal. Each timethe switch arm 12 is restored to normal thy-thespring 14 it leaves each button 13 and subsequently engages the nextsucceedin button intermittently toestablish a circu1t through theinterrupter relay 50 which through the winding of relay 49, the secondfrom the left of the armature switches of relay 47 and the.contact ofthis armature switch, the uppermost armature switch of relay 25 and itsnormal contact, the wiper 33 and its engaged waiting contact,- theuppermost armature switch of the cutofl relay 19 pertaining to thecalling line and its alternate contact, the upper side of the callingline, the telephone outfit at the calling station, the switch hook atthis station, the switch arm 12, the button 13 engaged by this switcharm, the switch 11, the contact of this switch, the lower side of thecalling line, the intermediate armature switch of said relay 19 and itsalternate contact, the wiper 32 and its engaged waiting contact, theintermediate armature switch of'relay 25 and its normal contact, theright hand armature switch of relay 47 next adjacent the winding of thisrelay, the contact of this switch, the winding of the interrupter relay50, to ground. The relay 49 is a sluggishly operating relay andmaintains its armature switches attracted after the button 17 has beenreleased and during the ensuing interruptions of the circuit includingthe switch arm 12, the movement of the arm 12 being sufficiently rapidto prevent the relay 49' from becoming effectively deenergized duringthe dialing operations. The lower armagnet 51 which is adapted tooperate a grounded wiper 52. When the relay49 is initially energizedupon the depression of the button 17 the wiper 52 is moved from one deadpoint toanother dead point and for each reestablishmentof the circuitthrough the arm 12 the wiper 52 IQOVGS astep. The waiting contacts ofthe Wiper52 ertain to a group of lines, the wiper 52 eing brought intoengagement with that waiting contact which is individual to the desiredline by means of the dialing opera-. tion at the calling station andwith the aid of the interrupter magnet 50 whose circuit is interruptedeach time the arm 12 is in cluded' in open circuit. After the desiredline has become associated with the wiper 52 the dialing operationceases and the relay 50 is maintained energized to attract its armotormagnet 51 0 case that the wiper 52 remains in association with thedesired line while the. lower armature switch engages its contact toestablish circuit for the motor magnet 53 of the connector switch, whichcircuit is traceable from the grounded battery 18 through the winding ofinterrupter relay 28 and its armature switch and contact, the lowerarmature switch of relay 50 and its contact, the extreme right hand 1 8aswitch of relay 47 and its contact, the motor magnet 53, the lowermostswitch of relay 25 and its normal contact, to the grounded resistance44. The-motor magnet 53 is now set into operation until its wipers 54,55, 56, and 57 engage waiting contacts belonging to the desired line, ifidle, the same line with which the wiper 52 has become associated, theextent of movement of the wipers 54, etc. being determined by thedialing operation at the calling station. The wipers 54, etc. arestopped in association with the desired line, if idle, as a consequenceof the establishment of a circuit traceable from the grounded battery58, the third armature switch from the left, of the relay 47 the contactof this switch, the lower winding of relay 25 the wiper 57, the waitingcontact of the id e desired line, the lowermost armature switch of therelay 19 of the desired line and its contact, the wiper 52 and itsengaged waiting contact, to ground. The relay 25 is thus energized tobring its lowermost armature switch intoengagement with its alternatecontact and out of engagement with its normal contact, the separation ofthis armature switch from its normal j contact opening the circuit ofthe motor magnet 53.- If the desired line is busy the circuit lasttraced cannot be established owing to the attraction of the lowermostarmature switch of the relay 19 of the desired line since the wipers 54,etc. will continue in operation either until the desired line agambecomes idle or until the calling subscriber restores his telephonereceiver upon its switch; hook.

When the lowermost armature switch of relay 25 engages its alternatecontact a circuit is established for maintaining the energization of thecutofi relay 19 of the called line, which circuit is traceable from thegrounded battery 18 through the winding of said relay 19, the wiper 31and its engaged waiting contact, the lowermost armature switch of relay25 and its alternate contact, to ground by way of theresistance 44 Thetwo upper armature switches of relay 25 include in circuit, at theiralternate contacts, the left hand winding of relay 59 which constitutesan impedance winding in bridge of the calling line, transmitter currentfrom battery 18 being fed to the calling line through this winding andthrough the upper windin' of relay 25 Transmitter current is also edfrom battery 18 through the right hand winding-of relay 59 which is animpedance winding and through the relay 60 by obvious connections .Whenthe relay 59 is energized ringing current is continued over the calledllne from the generator 45 by way of. the right hand intermediatearmature switch of rela 59, the normal follow-up contact of the owerarmature switch of relay 60, the wiper 55,

ture switch. When the called subscriber responds the low resistancetelephone bridge at his station shunts the high resistance bell bridgethereby;sufiiciently to increase the flow of current through the relay60 to cause this relay to attract its armature switches to connect thewipers 54 and 55 with the two upper armature switches of the relay 25and to break the ringing cir cuit at'the normal follow-u contact of thelower armature switch 0 the relay 60. When the relay 59. is energizedthe motor magnet 41 of the master switch common'to a plurality of linkconnectors each havin a relay 25 is included in circuit tracea le fromthe grounded battery 18, the winding of relay 21 the wiper 40 and itswaiting contact, the extreme left hand switch of the i-elay 59 and itscontact, to ground, whereupon circuit for the interrupter ma et 28 isintermittently established to continue the motor-magnet 41 in operationuntil the employed in establishing a connection between some new callingsubscriber and a desired line. The relay 47 individual to the relay 59is now deenergized to restore the elements 49, 50, 51, 52, etc. tonormal,

ice

the wiper 52 being restored to normal owing v to the function performedby the restoring magnet 61 whose circuit is artially established at 62upon the initial movement of the wiper 52 and which circuit alsoincludes the upper armature switch of relay 49 andits normal contact,and the grounded battery 18 .as will be apparent. The release magnet 61,when energized, attracts the armature that carries the actuating pawl 63then to permit the restoring spring 64 to brin the arm 52 to its normalposition, in whic position circuit is again opened'at 62 to cut themagnet 61 out of circuit after the restoring operation has beeneffected. "It is apparent that when the called party responds he cannotset either magnet'l or 2 into operation owing to the ener 'zation of hisrelay 19 which has been trace The system of my invention is not onlyadapted toenable the calling line to be connected with the called lineby either the manual or automatic equipment but obviously eitherequipment may be employed to connect thecalling line with differentcalled lines to which the other equipment does not have access and Ihaveillustrated this characteristic by the telephone line A extendingfrom the substation B having a jack l, the line A not having any waitingcontacts accessible to the wipers 54, etc. though the lines which areequipped with the jacks 4 do have such waiting contacts.

In the automatic equipment which I have illustrated there is shown oneselector switch (which includes elements 27 etc.) but it is obvious tothose skilled in the art that the capacity of the exchange maybeincreased by employing additional selector switches.

Most of the equipment illustrated at the exchange forms the subjectmatter of other applications and is not specifically claimed herein,though the provision of a circuit by which thecalling subscriber may benotified when to continue the dialing operation is thought to be a novelfeature of the exchange equipment at present shown.

While I have herein shown and particularly described the preferred formof my invention I do not wish to be limited to the precise details ofconstruction and circuit arrangement shown as changes may readily bemade without departing from the spirit of my invention.

Having thus described my invention I claim as new and desire to secureby Letters Patent the following 1 A telephone exchange system includingone telephone line extending from one telephone station to an exchange,there being a telephone receiver, a telephone transmitter and receiverswitch hook at this telephone station; additional telephone linesextending from other stations to an exchange; manual exchange equipmentfor connecting the first telephone line with one of the other telephonelines; electro-magnetic selecting switching mechanism for connecting thefirst telephone line with one of the additional telephone lines;exchange operators responsive apparatus pertaining to the aforesaidmanual equipment and made effective by the aforesaid switch hook whenthe receiver is removedfrom the switch hook; and a switch at theaforesaid telephone station having the switch hook and supplied inaddition to the switch hook and having control of the line circuit toenable it to effect the operation of the aforesaid electromagneticswitching mechanism to extend the line of the calling party.

In witness whereof, I hereunto subscribe my name this fourteenth day ofJanuary A. D. 1914.

ELMER R. CORWVIN.

Witnesses ETTA L. WHITE, G. L. CRAGG.

